1. Field of the Invention
The present invention relates to particle detection systems and, more particularly, to a particle detection system for detecting particles such as dust particles generated within semiconductor manufacturing systems.
2. Description of Conventional Art
In current semiconductor manufacturing processes, yields determine the price and reliability of products. Dust particles generated within a semiconductor manufacturing system have a considerable affect on yields, therefore the amount of dust generated within the semiconductor manufacturing system must be minimized in order to improve the yields. In other words, when semiconductor devices are produced in an environment containing a large amount of dust particles, the probability that the particles of dust adhere to wafers increases. As a result, product defects such as defective wiring patterns on the wafers increase, thereby decreasing yields. In the majority of currently used semiconductor manufacturing systems, dust particles are generated within the process chamber in the course of manufacturing the products, and the dust particles gradually accumulate in the process chamber. When the amount of dust particles exceeds a predetermined threshold value, product yield decreases below a predetermined value. As a result, profit is low even if the products are sold. Therefore, in the manufacture of semiconductor products it is necessary to always keep the amount of dust particles generated within the semiconductor manufacturing system under control and maintain the semiconductor manufacturing system when the number of particles exceeds the above-mentioned predetermined number (threshold) to remove the dust particles accumulated in the process chamber.
Among generally employed conventional methods of detecting particles such as dust is the light scattering method, which involves the steps of detecting, by means of a light-detection element, scattered light generated when a laser beam is radiated onto dust and measuring the number, size, etc. of the particles.
The light scattering method is also employed to measure dust generation within the semiconductor manufacturing system. A small-sized particle flux monitor disclosed in U.S. Pat. No. 4,804,853 is a prior art example employing the light scattering method for detecting dust in a semiconductor manufacturing system. The small-sized particle flux monitor disclosed in this patent is designed to measure the number and size of dust particles by focusing a laser beam emitted from a laser diode onto a dust detecting zone with a converging lens, scattering the laser beam when dust passes across the beam, and collecting the scattered light by means of photodiodes.
U.S. Pat. No. 4,739,177 proposes a particle detection system in which the probability of particle detection is improved by forming a laser beam net with a laser beam reflected between two mirrors. Further, U.S. Pat. No. 5,132,548 proposes a particle detecting system in which the probability of particle detection is improved by forming a sheet-like laser beam by means of a combination of prisms.
Since, generally, all the detecting system parts must be mounted and used inside the process vacuum chamber, a particle detecting system for detecting particles in a vacuum raises the following problems.
First, in the case of measuring particles in an etching gas environment such as a plasma etching system, the laser diode, lens, photodiodes, and the like mounted inside the detecting system deteriorate and shorten the lifetime of the detecting system to a significant degree. Further, these optical parts and the like are not only extremely expensive but also of high precision, so that a considerable amount of expense and labor are entailed in repairing them.
Still further, plasma CVD and sputtering systems are designed to deposit films by heating the wafer and the like, which subjects the process chamber to temperatures as high as several hundred degrees celsius. Parts of the detection system break at such high temperatures.
The above-mentioned small-sized particle flux monitor disclosed in U.S. Pat. No. 4,804,853 is mainly designed to detect floating particles in a gas or liquid with high responsivity. Therefore, such a monitor is not well suited to detect particles in a vacuum. Further, the detection systems according to U.S. Pat. Nos. 4,739,177 and 5,132,548 are of such a type that the sensor itself is installed in the process chamber. If these detection systems are mounted in the vacuum of the process chamber as they are, the detection systems themselves liberate gas, possibly adversely affecting the semiconductor products.
Further, if the above-mentioned detecting systems are used at high temperatures, the laser diode will fail, making it difficult to measure the dust within the process chamber of a plasma CVD or sputtering system. Still further, if the sensor is disposed within the process chamber in which a reactive gas is used such as in the process chamber of an etching system, the optical parts, including the lens in the sensor, may be eroded.
Still further, in order to maintain and repair the sensor, the process chamber must be exposed to the outer atmosphere, which entails a great deal of time and labor.
Dust particles are generated most in the process vacuum chamber such as the film deposition chamber or the etching chamber in the semiconductor manufacturing system. Therefore, the highest priority must be given to control of the generation of dust particles in the process chamber. While conventional dust particle detection systems can measure dust particles in the process chamber as described above, these systems cannot be used in reactive gas environments such as those used in etching systems or high temperature environments such as those used in plasma CVD systems.